[Mesa-dev] [PATCH 1/1] i965: Do not overwrite optimizer dumps

[Matt Turner]

On Wed, Nov 25, 2015 at 10:46 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Wed, Nov 25, 2015 at 10:45 AM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Wed, Nov 25, 2015 at 10:37 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>>> On Wed, Nov 25, 2015 at 10:31 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>>> On Wed, Nov 25, 2015 at 4:15 AM, Juan A. Suarez Romero
>>>> <jasuarez at igalia.com> wrote:
>>>>> When using INTEL_DEBUG=optimizer, each optimizing step is dump to disk,
>>>>> in a separate file.
>>>>>
>>>>> But as fs_visitor::optimize() and vec4_visitor::run() are called more
>>>>> than once, it ends up overwriting the files already on disk, loosing
>>>>> then previous optimizer steps.
>>>>
>>>> Huh. I guess this happens when non-orthogonal state changes and we
>>>> recompile the program?
>>>>
>>>> If so, yeah, that would lead to some confusing results.
>>>>
>>>>> To avoid this, add a new static variable that tracks the global
>>>>> iteration across the entire life of the program running.
>>>>> ---
>>>>>  src/mesa/drivers/dri/i965/brw_fs.cpp   | 13 +++++++++----
>>>>>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 11 +++++++----
>>>>>  2 files changed, 16 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>> index 29f19cc..9520a62 100644
>>>>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>>>> @@ -4947,6 +4947,8 @@ fs_visitor::calculate_register_pressure()
>>>>>  void
>>>>>  fs_visitor::optimize()
>>>>>  {
>>>>> +   static int global_iteration = 0;
>>>>
>>>> I don't know that adding a static variable is the way to solve this. I
>>>> know this is debugging code, but using a static variable will make
>>>> this thread-unsafe, and I *really* don't want to end up in a situation
>>>> where I can't figure out what the optimizer is doing because we were
>>>> compiling shaders in parallel...
>>>
>>> If we really care, we can use an atomic, but meh.  How often are you
>>> seriously using INTEL_DEBUG=optimizer on something that's compiling
>>> enough shaders in parallel for this to realistically be a problem?  I
>>> wouldn't want to dig through that many results.  But, like I said, if
>>> it bothers you, make it an atomic.
>>
>> That doesn't help.
>
> Then what thread-saftey issue are you concerned with here?

The code *reads* a global variable that might be changed by another
thread during the first thread's optimization loop.